Evaluation of the aging effect on mild steel (E 6013) welded areas using Hilbert Huang Transform on UT signals

The welding inspector ensures the integrity of weld joints since the structural stability mainly depends on it. Welded joints are tested for the prediction of remaining useful life using different Non Destructive Testing (NDT) schemes such as Ultrasonic Testing (UT). In this proposed study, possible classification of UT signals acquired from weld areas in terms of different levels of thermal fatigue were explored using Hilbert Huang Transform (HHT). The HHT was used to assess the aging effect by characterizing the ultrasonic backscattered echoes of scanned welded materials. The HHT being an empirical based method can generate meaningful representation of data from non-stationary and nonlinear system. Firstly, the ultrasonic signals were decomposed into a set of simpler signals called Intrinsic Mode Functions (IMF). Based on the Hilbert spectrum of these IMF, time-frequency analysis was conducted. Energy Frequency distribution based feature extraction was proposed for determining the aging effect of the welded material at particular locations.